PROJECT ABSTRACT Significant disparities in breast, cervical, and colorectal cancer mortality persist among marginalized populations, partially attributable to lower guideline concordant screening. Patient navigation is an evidence- based practice to improve adherence to cancer screening guidelines among marginalized populations in order to reduce cancer disparities. Cancer screening navigation activities may be implemented using professional (e.g. nurse) or lay (e.g. community health worker, CHW) navigator models, the latter in clinical or community settings. Implementation of CHW-led cancer screening navigation is more feasible in low-resource settings compared to nurse-led cancer screening navigation and is associated with improved screening outcomes. However, we lack a comprehensive understanding of how this is accomplished, both from the perspective of CHWs as well as from the perspective of the clients they serve. Furthermore, rigorous evaluation of CHW-led cancer screening activities in relation to screening outcomes is lacking. The purpose of this study is to characterize factors that affect implementation of cancer screening navigation activities by CHWs in the context of the National Breast and Cervical Cancer Early Detection Program (NBCCEDP) and the Colorectal Cancer Control Program (CRCCP), two federal screening programs established to provide vulnerable populations access to timely cancer screening and diagnostic services. Using the Consolidated Framework for Implementation Research (CFIR), we will identify implementation domains that affect CHW-led cancer screening navigation including: outer setting (e.g. program policies), inner setting (e.g. CHW training), and individual characteristics (e.g. CHW social support) via key informant interviews with CHWs (n=25). We will compare domains across cancer- (i.e. breast, cervical, and colorectal) and community-type (i.e. urban and rural) to understand potential differences. We will also recruit program clients of CHWs (n=250) to study associations between the presence, type, intensity, and quality (e.g. client satisfaction) of CHW-led cancer screening navigation activities as well as subsequent screening outcomes over a one-year period. Finally, we will use community-based participatory research (CBPR) principles to engage program stakeholders at all stages of the research process which will culminate in a consensus conference to generate best practices for the implementation of CHW-led cancer screening navigation activities. These findings will inform multi-level health service interventions to improve the effectiveness of cancer screening navigation using CHW models of delivery. The proposed career development in implementation science, leading practice-based research, and applying and evaluating CBPR processes will prepare the candidate to excel as an independent researcher focused on addressing cancer disparities in partnership with marginalized communities and health systems.